An investigation of mechanical degradation of AlMg1SiCu aluminum alloy by hydrogen

Abstract

The mechanical degradation of AlMg1SiCu aluminum alloy by hydrogen was investigated using experiments conducted on specimens that were hydrogen charged under different cathodic charging conditions. Cathodic hydrogen charging was found to reduce the ultimate tensile strength, yield strength and ductility of aluminum alloy. These parameters decreased with increasing cathodic current density and charging time. However, it was found that cathodic hydrogen charging for longer time resulted in more reduction of tensile properties than that at higher current density. Moreover, mixed mode of hydrogen cracking (i.e. intergranular and transgranular) as well as gas bubbles were observed during first charging condition while only intergranular cracking was observed during the second charging condition. Furthermore, hydrogen cracks formed during long-charging time are extended deeper within aluminum alloy specimens than those formed during high current charging condition. The aluminum hydride formed during cathodic charging was found to contribute to hydrogen embrittlement of aluminum alloy. Microhardness measurements revealed that the introduction of hydrogen caused hardening on the surface of aluminum alloy. The severity of hardening increased with either cathodic current density or charging time. Further charging increased the depth of the hardened region of aluminum alloy. Natural ageing after charging resulted in either complete or partial recovery of hardness, ultimate tensile strength and yield strength depending on the prior hydrogen charging conditions. However, the tensile ductility of hydrogen-charged aluminum alloy was not recovered to its original value (i.e. before charging) even after prolonged natural ageing.